Coin type batteries are widely used as power sources for small apparatuses or memory backup. The application of the coin type batteries is continually expanded. So, countermeasures against accidental ingestion of a coin type battery become more important. When a coin type battery will be is swallowed into a living body, contacting the terminal surface of each of a case and a sealing plate of the coin type battery comes with a body fluid result in proceeding electrolysis of water. pH of body fluid is around neutral. When the electrolysis of water proceeds, the body fluid near the terminal surface on the negative electrode side shift to alkaline, and the body fluid on the positive electrode terminal side shift to acidic. Therefore, the living body is damaged.
From the viewpoint of preventing accidental ingestion, Patent Literature 1 proposes forming a conductive film containing a bitter substance on a battery surface.